1USB Legacy support
2~~~~~~~~~~~~~~~~~~
3 4Vojtech Pavlik <vojtech@suse.cz>, January 2004
5 6 7Also known as "USB Keyboard" or "USB Mouse support" in the BIOS Setup is a
8feature that allows one to use the USB mouse and keyboard as if they were
9their classic PS/2 counterparts. This means one can use an USB keyboard to
10type in LILO for example.
11 12It has several drawbacks, though:
13 141) On some machines, the emulated PS/2 mouse takes over even when no USB
15 mouse is present and a real PS/2 mouse is present. In that case the extra
16 features (wheel, extra buttons, touchpad mode) of the real PS/2 mouse may
17 not be available.
18 192) If CONFIG_HIGHMEM64G is enabled, the PS/2 mouse emulation can cause
20 system crashes, because the SMM BIOS is not expecting to be in PAE mode.
21 The Intel E7505 is a typical machine where this happens.
22 233) If AMD64 64-bit mode is enabled, again system crashes often happen,
24 because the SMM BIOS isn't expecting the CPU to be in 64-bit mode. The
25 BIOS manufacturers only test with Windows, and Windows doesn't do 64-bit
26 yet.
27 28Solutions:
29 30Problem 1) can be solved by loading the USB drivers prior to loading the
31PS/2 mouse driver. Since the PS/2 mouse driver is in 2.6 compiled into
32the kernel unconditionally, this means the USB drivers need to be
33compiled-in, too.
34 35Problem 2) can currently only be solved by either disabling HIGHMEM64G
36in the kernel config or USB Legacy support in the BIOS. A BIOS update
37could help, but so far no such update exists.
38 39Problem 3) is usually fixed by a BIOS update. Check the board
40manufacturers web site. If an update is not available, disable USB
41Legacy support in the BIOS. If this alone doesn't help, try also adding
42idle=poll on the kernel command line. The BIOS may be entering the SMM
43on the HLT instruction as well.
44 45